“A blood-orange blob the size of a small refrigerator emerged from the dark waters, its venomous tentacles trapped in a fishing net. Within minutes, hundreds more were being hauled up, a pulsating mass crowding out the catch of mackerel and sea bass.

The fishermen leaned into the nets, grunting and grumbling as they tossed the translucent jellyfish back into the bay, giants weighing up to 200 kilograms (450 pounds), marine invaders that are putting the men’s livelihoods at risk.

The venom of the Nomura, the world’s largest jellyfish, a creature up to 2 meters (6 feet) in diameter, can ruin a whole day’s catch by tainting or killing fish stung when ensnared with them in the maze of nets here in northwest Japan’s Wakasa Bay.”

“The invasions cost the industry up to 30 billion yen ($332 million) a year, and tens of thousands of fishermen have sought government compensation, said scientist Shin-ichi Uye, Japan’s leading expert on the problem.”

“He concluded China’s coastal waters offered a perfect breeding ground: Agricultural and sewage runoff are spurring plankton growth, and fish catches are declining. The waters of the Yellow Sea, meanwhile, have warmed as much as 1.7 degrees C (3 degrees F) over the past quarter-century.

“The jellyfish are becoming more and more dominant,” said Uye, as he sliced off samples of dead jellyfish on the deck of an Echizen fishing boat. “Their growth rates are quite amazing.”

“A U.S. marine scientist, Jennifer Purcell of Western Washington University, has found a correlation between warming and jellyfish on a much larger scale, in at least 11 locations, including the Mediterranean and North seas, and Chesapeake and Narragansett bays.

“It’s hard to deny that there is an effect from warming,” Purcell said. “There keeps coming up again and again examples of jellyfish populations being high when it’s warmer.” Some tropical species, on the other hand, appear to decline when water temperatures rise too high.”